This invention pertains to electrical testing of protective linings of steel pipes, vessels, and other liquid containers, and is more particularly concerned with the structure of an electrode probe assembly for performing such tests.
Steel containers such as vessels and pipes are widely used in the food and chemical industries for processing liquids. A protective lining of material such as glass, plastic, or rubber is often required to separate the steel shell of the container from the corrosive effect of the liquid. It is important that the lining be free of defects or faults because if contact were to be made between liquid and shell, the steel would corrode and possibly result in the failure of the steel container. Also, corroded steel particles would contaminate the liquid product.
For those reasons electrical fault finders have been used for detection of defective linings, eliminating unexpected, possibly catastrophic, vessel failures and allowing the transfer of the liquid product to another vessel before iron contamination becomes critical. In either case, repairs to the lining can be made before permanent, irreparable damage results.
An intact lining functions as an electrical insulator between the conductive liquid product and the steel. This property can be utilized in testing for defects.
One approach to detect faults in the lining is to actively impress a voltage between an electrode immersed in the conductive liquid and the steel shell which contains the liquid. Current flow indicates a defect in the lining. Alternatively, passive galvanic fault finders may be used.
Galvanic fault finders operate on the principle that dissimilar metals electrically connected together and immersed in a conductive liquid (electrolyte) develop a voltage between the metals. The galvanic fault finder detects this voltage or the current produced. U.S. Pat. Nos. 3,831,058 and 3,858,114 describe an arrangement wherein a platinum electrode is immersed in the electrolyte liquid contents of a lined steel vessel. The platinum electrode must be electrically insulated from the steel shell. If the liquid contents of the vessel or pipe makes contact with the steel shell a voltage occurs between shell and electrode. Monitoring this voltage or the resultant current provides indication of a fault.
A significant difficulty with the typical probe assemblies of the prior art (exemplified in FIG. 3) is leakage and/or breakage of the electrode which is made from tantalum alloy. This material is very brittle and over-tightening the electrode easily causes breakage. The acceptable tightening torque is very low. Also, when the electrode is installed, a polytetrafluoroethylene (PTFE) gasket is compressed to make a liquid-tight seal. However, if the electrode has sharp edges, the electrode may cut through the gasket as it is screwed in. Another problem is the relaxation of the PTFE gasket over time and temperature. Both difficulties result in possible leakage of the probe installation.
An object of the invention is to provide a fault finding electrode completely isolated from conduction members such as flush valve assemblies or baffles.
Another object of the invention is to provide an electrode assembly having an electrical circuit which is immune to corrosive humidity and water.
Another object of the invention is to provide an electrode assembly that does not cut a sealing gasket.
A further object of the invention between an electrode is to maintain a liquid-tight seal assembly and its mounting member even if the gasket relaxes.